The present invention relates to a developing device comprising a developing unit that develops an electrostatic latent image formed on an image carrier through an electrophotographic recording system or an electrostatic recording system to be a visual image using developer and a toner supply unit that supplies toner to the developing unit.
In general, in an electrostatic image forming apparatus such as an electrophotographic copying machine or the like, an electrostatic latent image on a charge-carrier (a photoreceptor drum and others) is developed to be a visual toner image in a developing device, and then the visual toner image is transferred onto a recording sheet to be fused thereon so that a copy image may be formed.
Heretofore, as a developing method for an electrostatic latent image formed on a photoreceptor drum, there has been used widely a magnetic brush type developing device employing a two-component developer consisting mixedly of toner and magnetic carrier or a single-component developer. In the magnetic brush type developing device, a developing roller composed of a cylinder-shaped non-magnetic developing sleeve and a plurality of permanent magnets provided inside the developing sleeve is positioned to be away from an image carrier with a fixed gap between them, and developers adhering magnetically to the circumferential surface of the developing sleeve are conveyed through the rotation of the developing sleeve to a developing area which faces the image carrier for the development of the electrostatic latent image.
In the developing device wherein the two-component developer mentioned above is used, when copying is repeated, toners in the developing device are consumed. Accordingly, when toners equivalent in quantity to the consumption amount are not supplied and thereby the mixture ratio of toners to carriers (toner concentration) is not kept constant, copies having appropriate density can not be obtained. Therefore, the developing device is constituted so that the mixture ratio of toners to carriers in the developing device may be detected and thereby toners may drop to be supplied automatically by a toner supply unit.
On the other hand, developers contained in the developing device, after being used in copying for the number of times, cause a copied image to be deteriorated in image quality because of deterioration in performance of the developers caused by fatigue of carriers therein and by mixing of foreign materials such as paper dust and others. Therefore, when conducting a regular maintenance after making copies in predetermined quantity (for example, 10,000-30,000 copies), or when problems happen on the developer for some reasons, the developer is required to be replaced completely by putting fresh two-component developer in the developing device after discharging the total amount of the developer contained in the developing device.
Incidentally, single-component developer is also replaced in the similar manner.
When the electrostatic image forming apparatus is shipped from a factory, or when it is transported over the long distance, the apparatus is shipped or transported with no developers in the developing device, and developers are filled in the developing device after the image forming apparatus has been installed.
In general, when the developers are put in or replaced completely, fresh developers are poured through an opening formed by a cover on the top of the developing device. When pouring the developers, a part of them tend to flow out or scatter over the outskirts of the opening, resulting in troublesome cleaning thereof.
Since the opening is in the vicinity of the photoreceptor drum, in particular, care must be taken for the scattering of or contamination by the developers.
Further, since the space above the developing device interferes with an optical path through which the image light flux from an exposure unit of a copying machine passes to form an image on the photoreceptor drum, it is not possible to provide a hopper-shaped developer-pouring inlet on the cover of the developing device. Accordingly, it has been compelled to pour developers by dismounting a toner supply unit adjoining the developing device and thereby causing the opening to be exposed.